1. Field of the Invention
The present invention relates to a thin-film magnetic head comprising a magneto-resistive effect device for reading the magnetic field strength of a magnetic recording medium or the like as signals, and a head gimbal assembly and a magnetic disk system, each comprising that thin-film magnetic head.
2. Explanation of the Prior Art
In recent years, with an increase in the plane recording density of magnetic disk systems, there have been growing demands for improvements in the performance of thin-film magnetic heads. For the thin-film magnetic head, a composite type thin-film magnetic head has been widely used, which has a structure wherein a reproducing head having a read-only magneto-resistive effect device (hereinafter often called the MR device) and a recording head having a write-only induction type magnetic device are stacked together.
The MR device, for instance, includes an AMR device harnessing the anisotropic magneto-resistive effect, a GMR device making use of the giant magneto-resistive effect, and a TMR device taking advantage of the tunnel-type magneto-resistive effect.
Requirements for reproducing heads, among other, are high sensitivity and high output. For reproducing heads meeting such requirements, GMR heads using a spin valve type GMR device have already been mass produced.
Further, GMR devices of the structure with sense currents flowing perpendicularly to the plane of each of their constituting layers, viz., GMR devices of the CPP (current perpendicular to plane) structure (CPP-MR devices), too, are now under development as coming-generation ones. TMR devices now in full commercial production and practical use, too, fall under the category of CPP-MR devices.
In a thin-film magnetic head comprising such a magneto-resistive effect device, there are two bias magnetic field-applying layers provided, one on each side of the magneto-resistive effect device. By way of these bias magnetic field-applying layers, the so-called longitudinal bias is applied to the device so that a given external magnetic field can be detected while noises are staved off.
Referring here to a thin-film magnetic head comprising a prior art magneto-resistive effect device, FIGS. 14 and 15 are illustrative of in what relations the rear end of the magneto-resistive effect device and the rear end of a bias mechanism portion including bias magnetic field-applying layers are positioned. FIG. 14 is illustrative in plane of in what states a conventional magneto-resistive effect device 505 and a prior art bias mechanism portion 506 are disposed, and FIG. 15 is a plan view of another prior art example illustrative of in what states the magneto-resistive effect device 505 and bias mechanism portion 506 are positioned.
(1) As shown in the plan view of FIG. 14, the rear end 505a of the magneto-resistive effect device 505 and the rear end 506a of the bias mechanism portion 506 have been processed by Ar ion milling, using a mask prepared in such a way as to bring that rear end 505a in alignment with that rear end 505b; and
(2) as shown in the plan view of FIG. 15, the rear end 505a of the magneto-resistive effect device 505 and the rear end 506a of the bias mechanism portion 506 have been processed while the length of the bias mechanism portion 506 out to the rear end 506a is much longer than the length of the magneto-resistive effect device 505 out to the rear end 505a (the so-called wide type of bias mechanism portion), so that the rear end 506a of the bias mechanism portion 506 is positioned more on the depth-wise side than the rear end 505a of the magneto-resistive effect device 505.
In the aforesaid case (1), it is likely that the taper angle of the rear end 506a of the bias mechanism portion 506 that inclines in its thickness direction (the depth-wise direction of the sheet of FIG. 14) may be equal to or larger (more precipitous) than the taper angle of the rear end 505a of the magneto-resistive effect device 505. Therefore, no large enough bias magnetic field can likely be applied to near the rear end 505a of the magneto-resistive effect device 505 that is an unsteady magnetization area (the rear end of a free layer in particular). Consequently, there is inconvenience of magnetic noises being likely to occur.
In the aforesaid case (2), a large enough bias magnetic field can be applied to near the rear end 505a of the magneto-resistive effect device 505 that is an unsteady magnetization area (the rear end of a free layer in particular), too, so that noises can be controlled. In the case (2), however, it is required that the rear end 505a of the magneto-resistive effect device 505 and the rear end 506a of the bias mechanism portion 506 be independently formed. This means that there is the need of readying up two process steps for the formation of those rear ends, making the process involved awkward. Moreover, for that process high position precision is needed because of a change in the bias strength depending on the relative position of the magneto-resistive effect device 505 and bias mechanism portion 506.
The situation being like this, an object of the invention is to provide a thin-film magnetic head comprising a magneto-resistive effect device, which is fabricated in an easier manner, enables the rate of occurrence of noises to be kept lower, and makes sure higher reliability and fabrication yields.